| Author |
Message |
james dean boggs (Jd_boggs)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, February 10, 2006 - 9:55 pm: | |
My 1981 Grumman/Flex's brakes are working well as far as I can tell. Just replaced the air dryer cartridge and would like to replace the brake chambers but I dont want to fix something that's not broke. What is the rule for replacing the chambers? |
Phil Dumpster2
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, February 10, 2006 - 11:04 pm: | |
When they get rusty enough to compromise their operation, or when they start leaking.
Some fleets replace them after a certain amount of time even if they look OK and work OK. |
Geoff (Geoff)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, February 11, 2006 - 10:01 am: | |
If the brake pods look okay, what you want to do is replace the rubber diaphrams. Be carefull when doing the double chamber pods(30/30's), you have to use the spring compression screw to change out the parking brake diaphram. If you don't know what I am talking about, leave it alone!
--Geoff
'82 RTS AZ |
Jim Shepherd (Rv_safetyman)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, February 11, 2006 - 10:45 am: | |
As Geoff points out, it is easy and inexpensive to rebuild the chambers. Also as he points out, do not try to rebuild a spring brake, as it can really hurt you if you don’t know how to rebuild them (when the spring is not caged).
I have posted this before, but it is worth posting again. When I worked for the Gates Rubber Company, one of my assignments was to manage the various test labs. We had an extensive brake diaphragm test facility. We tested the diaphragms by working two sets of brake chambers against each other. While the objective was to measure the life of the diaphragms, we also had CHAMBER FAILURES. The chambers are always undergoing pressure cycles and that results, ultimately, in fatigue failures. I remember vividly that one of the technicians was right next to one when it let loose and bounced off the wall beside him.
OK, what does all of that minutia say? Well, both diaphragms AND Chambers can fail. If a diaphragm fails, it usually starts as a slow leak and gets worse (usually fairly quickly). If it is a slow leak, it will still work. If the chamber fails, you have a total loss of braking on that axle.
Admittedly, you can go through several diaphragms before the chamber needs to be replaced. However, most of us don’t know the history of our bus and the brake system maintenance. A new chamber is not very expensive, and it is probably worth thinking about changing the complete chamber rather than rebuilding it.
Inspection of the brake chamber system is difficult. About the only thing you can do is to have someone apply full brakes and listen for any leaks from the chamber. That still does not tell you if they will begin leaking or fail on the next application of brakes. Given the safety/liability issues involved it is probably worth it to replace all of the non-spring brake chambers as a preventative maintenance measure.
Jim Shepherd
Evergreen, CO
’85 Eagle 10
http://rvsafetysystems.com Toll Free: 1**888**349**0704
Bus Project details: http://www.rvsafetysystems.com/busproject.htm (updated 2/9/06) |
Dale Waller (Happycampersrus)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, February 11, 2006 - 10:54 am: | |
NAPA has 30/30 chambers for around $40 to $50.
If one diaphram blows out the other chamber diaphram isn't far behind. On the Double chambers you don't want to try to open the emergency side. It has a very large spring that will cause severe injury if you don't know what you are doing.
You can change the service brake pancake if you "cage the spring". Use the special bolt that goes in the hole on the back of the chamber to to compress the spring.
I used to try to fight and just change the "pancake" diaphrams just to have the other side blow out a few weeks later. It so much easier to get new chambers and have peace of mind knowing the age and condition of them.
Just because they look good that doesn't mean they are not 10 years old with 150K miles on them.
Gus Hill trucking (50+ trucks & trailers)change theirs every 100K miles I believe
FWIW,
Dale |
Jon W.
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, February 11, 2006 - 11:31 am: | |
The recommended change interval for brake chambers is 1 year or 100,000 miles. I'm not saying I support this, but for commercial operators it is probably a safe recommendation.
I have had the cans rust and I have had diaphragm failures so I would not bother messing with a diaphragm replacement. The last ones I changed I pulled apart the cans and due to a lousy paint job, the plunger the diaphragm pushes against had bubbled up rust on the surface and continued use would likely result in wearing through the area of the diaphragm where it pushes against the plunger.
The chambers were from an 8 year old Prevost with about 160,000 miles and were changed just to bring everything up to new condition.
For as cheap as these things are it isn't worth waiting until they start to fail. The alternative is scary to consider. |
james dean boggs (Jd_boggs)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, February 11, 2006 - 10:15 pm: | |
Thanks for the helpfull information. I have read many threads about brake chambers and know NOT to mess with springs. I have also read all information that Bendix has and my bus maintenance manuals. I figure it's easier to just replace the entire assembly however, I have concerns about rod travel adjustments and the automatic slack adjuster. Having seen the mechanical drawings of the assembly, it is easy to understand. I'm confident that I can do it but will I do it right? |
John Jewett (Jayjay)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, February 11, 2006 - 11:17 pm: | |
Not sure if you can do it right? Then take your handy-dandy little digital camera and shoot a handfull of photos before you start, and during the disassembly process. If need be, you can print a few to take out to the jobsite. It'll be a piece of cake, since you also have the manuals.
Cheers...JJ |
Jon W.
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, February 12, 2006 - 10:12 am: | |
JD,
Fear not. You can cut the threaded rod to your required length just by matching your existing chambers.
The only thing you need to do to deal with the self adjusting slack adjusters is to loosen them if necessary and it may not even be necessary.
If you want photos on how to release and loosen the slack adjusters let me know and I can email some photos with an explanation. |
james dean boggs (Jd_boggs)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, February 12, 2006 - 8:58 pm: | |
Thanks for the confidence builders! I'll take your advice and snap pics BEFORE I do anything. The manual says it has Bendix Type 20 on the front and 30/30 in rears but last time I ordered parts for this bus the parts manual lied to me so I'll have to remove on front and one rear for matching. |